Objective / Rules- You have to complete the grid such that every row and column contains the numbers 1 to 4 (each number appears exactly once).- The symbols on the grid indicate neighbours (e.g. 1 >< 2, 3 >< 4, 2 >< 1).- Rule 1 - if there is a symbol the numbers are neighbours.- Rule 2 - if there is NOT a symbol the numbers are NOT neighbours.- The Hard puzzles can be very hard.

Keyboard Usage[only when your cursor is in the grid]Note: not all options work on all browsers.A = auto-pencil marks (or click the check box below the puzzle).CTRL + arrows = move around the grid.SHIFT + number = highlight all squares with that number as a pencil mark [SHIFT+0 to clear].

Mouse UsageClicking a neighbour symbol will change its colour, very useful when you know the symbol has been satisfied."Show squares with a..." highlights all squares with that number as a pencil mark.

CheckingIf you click 'Check' the system will check for incorrect squares. If 'Show mistakes when checking' is checked they will be marked in red. There are two types of error checked for:1. A single number that isn't the same as the solution.2. Multiple numbers that don't contain the solution number.

UniquenessEach puzzle has exactly one solution, which can be found using logic alone and no guesses are ever required. If you think you've found another solution, then please double check the rules. If you still think you've found another solution, then please email us and we'll try to help.